The present invention is directed to the asymmetric epoxidation of prochiral ethylenically unsaturated substrates. The epoxides obtained by the process of this invention are optically active and useful as synthetic intermediates in the preparation of a wide variety of physiologically active products. U.S. Pat. Nos. 4,471,130 and 4,764,628 teach to epoxidize allylic alcohols using racemic or achiral alkyl hydroperoxides and titanium complexes containing optically active alkoxide substituents as catalysts.
Rebek et al [J. Org. Chem. 43, 180(1978); J. Am. Chem. Soc. 102, 5602(1980)]disclose the epoxidation of olefins with optically active peroxy compounds derived from ketals, Schiff bases, or isoindolones. Only a low degree of asymmetric induction (&lt;10% e.e) was observed.
Takata et al [Bull. Chem. Soc. Jpn. 59, 1275(1986); Tetr. Lett. 27, 1591(1986]teach the asymmetric oxidation of sulfides with optically active peroxy compounds prepared by singlet oxygenation of thiazolidine derivatives. The optical purity of the sulfoxide products was moderate at best (.ltoreq.37% e.e.).
It is clear that a need exists for alternative synthetic methods by which ethylenically unsaturated substrates may be epoxidized in an asymmetric manner to yield optically active products.